Eugenol "purified" by HPLC20 was compared to commercial USP eugenol to determine if any difference exists between the inflammatory response caused by each. Mixtures of each eugenol with zinc oxide were also compared. Each material was injected subcutaneously beneath the abdominal skin of 40 Walter Reed white rats. Ten animals were sacrificed at four different dates, and the degree of necrosis and inflammation was compared. The purified eugenol caused less necrosis and inflammation at all times than did the commercial eugenol. The purified ZOE mixture produced less necrosis and inflammation than the commercial ZOE mixture at each sacrifice date. The two mixtures of ZOE and the two samples of eugenol produced roughly parallel amounts of inflammation, suggesting that the degree of inflammation of ZOE mixtures is strongly influenced by the amounts of free eugenol in the mixtures. This study suggests that the impurities in commercial eugenol do cause an increase in the inflammatory response in the rat system studied. This increase is most evident at day two and after day ten.